Automatic telephone selector



May 20, 1941. B. J. BRANDER AUTOMATIC TELEPHONE SELECTOR Filed May 3,1938 2 Sheets-Sheet l .B. JBranaQeP May 20, 19.41. B. J. BRANDERAUTOMATIC TELEPHONE SELECTOR Filed May 3, 1938 2 Sheets-Sheet 2 I N vewfor Patented May 20, 1941 AUTOMATIC TELEPHONE SELECTOR Bertil JohanBrander, Stockholm, Sweden, as-

signor to Telefonaktiebolaget L. M. Ericsson, Stockholm, Sweden, acompany of Sweden Application May 3, 1938, Serial No. 205,837 In SwedenMay 5, 1937 6 Claims.

The present invention relates to telephone selectors oi the kind inwhich the selecting mechanism is adapted to cooperate with a multiplefield consisting of bare wires. More particularly the invention relatesto such telephone selectors in which the selecting mechanism comprises amember, preferably in the form of a chariot or carriage, which ismovable in a straight path in front of the multiple field and isprovided with a number of contact arms or wipers adapted to be insertedbetween the bare wires of the multiple field. In selectors of said kindthe wipers thus perform two distinct movements in directions extendingat right angles to each other, namely a first movement during thedisplacement of the carriage to select a certain group of wires in themultiple, and a second movement when the wipers are inserted between themultiple wires to select a certain line within the group.

According to the invention selectors of the kind set forth are providedwith wipers in the form of flexible electric conductors, for instancethin elastic metal bands or metal wires, which are movable inperpendicularly bent paths in the carriage in such a manner that whenthe carriage is stationary a force which acts in the direction ofmovement of the carriage can be used for pushing the flexible conductorsalong said paths and further into the multiple field in a direction atright angles to the direction of movement of the carriage. By arrangingthe wipers in this manner complicated movement transmitting mechanismfor efl'ecting the two different setting movements of the wipers may bedispensed with.

The invention will now be described more in detail having reference tothe drawings attached to this specification and forming part thereof, inwhich Figure 1 is a front view of an embodiment of a selector accordingto the invention,

Figure 2 is a top view thereof,

Figures 3 and 4 show two sections through the selector on the lines A-Aand B-B respectively, and

Figures 5 and 6 show details of a wiper.

The selector is intended for use in connection with a. multiple fieldconsisting of bare metal wires that extend vertically and are arrangedin groups of square cross-section, as shown in Figure 2.

The movable switching members of the selector comprise two main partswhich are movable back and forth rectilinearly, namely a chariot orcarriage a and a slide b. The carriage it consists mainly of a metalplate I which by means of four depending lugs 2 is displaceable alongtwo gtiide rods 3 secured to the bottom plate 0 of the selector, and ofa plate 4 of pressure-cast insulating material, for example of thematerial sold under the trade name Bakelite, said plate 4 being securedonto the plate I. The Bakelite plate 4 is provided with four narrowslots or channels in which four elastic metal bands 5 (for exampleconsisting of steel or of a stainless steel alloy) are readily slidablc.Said metal bands 5 form the wipers or contact arms of the selector, eachmetal band being provided at its outer end with a kind of plug 6 ofinsulating material intended to be inserted between the wires of themultiple field. The inner ends of the metal bands 5 are secured on theslide b so as to be insulated therefrom and form together with the slidea system which is movable back and forth in a straight path. The slide bis movably supported by means of a metal loop 1 on a bar 8 secured inthe bottom plate 0 and it is coupled with a bar l0 which is movablebetween four rollers 9 mounted in such positions on the bottom plate cas to permit an arm ll secured on the bar Ill to engage with a pin I2inserted in the loop I. The bar I0 thus also forms a part of the systemwhich is movable together with the slide b.

Secured on the bar i0 is a rack l3 which is in engagement with a pinionl4 mounted on the shaft of a small motor d serving to drive theselector. The construction of the motor d is arbitrary as long as itpermits of driving the rack l3 together with the slide b back and forthby means of current impulses.

Each of the plugs 6 is provided with a contact spring 15 electricallyconnected with the corresponding metal band, said contact spring beingadapted upon insertion of the plug into the bank of contacts to makecontact successively with said wires. The contact spring can also beformed by the metal band 5 proper, provided that the end of said band isgiven a shape suitable for making contacts.

The carriage a is actuated by a comparatively Weak helical spring l6which is threaded onto one of the guide rods 3 and which engages at oneof its ends with an adjustable stop on the guide rod 3 and presses atits other end against the bent-over edge of the plate I. The helicalspring l6 thus strives to move the carriage towards its position ofrest. Mounted on the carriage a is also a detent I! which by means of apin or projection extending towards the bottom plate engages with atoothed bar l8 which is secured on the bottom plate 0. For closing thechannels in the carriage a a cover plate 27 is mounted on the plate 4,

Arranged on the bottom plate c are three contact spring groups 6, f, g,of which e and serve to interrupt a circuit in the position of rest ofthe selector, and 9 serves to close a relay circuit provided forreversing the direction of movement of the motor when during itsrestoring movement the carriage a has arrived in its outermost position(to the left).

The co-operation of the various parts will appear from the followingdescription of the manner of action of the selector.

The selector illustrated on the drawings is assumed to be a finalselector for a system comprising 100 subscribers lines and its manner ofaction is as follows:

When the subscriber has been connected in known manner by means of aline selector to the final selector, impulses arrive from the dial inknown manner in the form of current interruptions in the line, arepeating relay set then transferring the impulses in such a manner thatthe stator electro-magnets i9, 20, 2| of the motor obtain in rotationone impulse each for each impulse from the dial. The rotor of the motorthen rotates one half revolution (clock-wise) bringing about thedisplacement of the rack l3 a distance to the left which is equal to thepitch of the conductor groups in the multiple field. The rack bringsalong the slide 1) and together therewith the bar It, the bar in turnbringing along the carriage a by means of the metal bands 5, so that theplugs 6 become displaced one step to the left in front of the multiplefield. The same operation is repeated for each impulse from the dial,the plugs 6 being thus set in position right opposite to the wantedconductor group in the multiple.

During the displacement of the carriage a to the left the detent l'lfreely slides over the teeth of the toothed bar l8, stopping in a toothopening corresponding to the position of the plugs 6, the pitch of theteeth being equal to the pitch of the conductor groups in the multiplefield. Upon cessation of the first train of impulses a relay, which isadapted to prepare in advance the rotation of the motor armature in thereverse direction, is energized in known manner by means of aslow-upon-release relay which remains attracted during the entire trainof impulses but thereafter drops its armature. The following train ofimpulses will therefore bring about a displacement of the rack IS in theopposite direction (to the right) a number of steps equal to the numberof impulses in the train of impulses now received by the impulse relay.The slide 1) is also displaced to the right and since the carriage a isprevented by the detent mechanism. l1, Hi from being displaced as well,the metal bands 5 will slide in their slots in the carriage a causingthe plugs 6 to be moved in between the multiple wires a number of steps,equal to the number of impulses in the last train of impulses. Thesetting of the selector on the wanted line is now completed.

The restoring of the selector to its position of rest is effected bymeans of two trains of impulses which are automatically supplied to themotor. The first train effects a rotation of the motor armatureclockwise with a consequent displacement of the slide b to the left.During this movement the metal bands 5 with their plugs 6 are firstpulled out from the multiple field, and when this has been done and theplugs 6 have reached their bottom positions in the Bakelite plate 4 thecarriage a will follow the movement of the slide b until the detent IThas passed over the last or eleventh tooth of the toothed bar l8. Atthis moment the contacts between the contact springs of the spring group9 are closed by means of an insulated metal pin 22 on the carriage a,causing a so called reversing relay to operate and to bring about arotation of the motor d in the opposite direction. This will cause theslide 2) to be driven to the right together with the carriage a, thedetent ll of the carriage then sliding along the opposite edge of thebar l8 until the members a and b have reached their positions of rest,when the operating current of the motor is interrupted through openingof the contacts in the spring groups e and f.

The helical spring l6 which strives to move the carriage a towards itsposition of rest has for its purpose to insure the restoring of theselector in that, first, it prevents the carriage from starting to moveto the left on the pulling out of the plugs from the multiple fielduntil the plugs have reached their positions of rest and, second, itprevents the metal bands from being pushed out anew on reversal ofmovement of the motor, as could otherwise happen if for some reason thefrictional resistance between the carriage a and the guide rods 3 shouldbe greater than the resistance offered by the metal bands 5 when pushedout towards the multiple field. If, however, said two factors arecorrectly balanced with respect to each other the helical spring Hi canbe dispensed with, entailing the advantage of reducing the load of themotor during the first setting movement of the selector. Alternatively,the slide 1) can be provided, instead of with the helical spring l6,with a detent which engages with a fixed toothed rod similar to thetoothed rod I 8 but having its teeth turned in the opposite direction,said detent being held out of function during the simultaneous movementsof the slide b and the carriage a by means of an arm or a projectionprovided on the carriage to be released on the reversed movement of theslide 1) then looking the carriage a until the slide 1) has returned toits position of rest with respect to the carriage.

The plugs 6 are preferably made of a cast insulating composition(Bakelite) and are I-shaped in cross-section, as will be clear fromFigure 5.

The flanges which project on opposite sides of each contact spring l5serve as guides during the movement of the plug between the multiplewires; it should be noted that during the movement of the plug saidfianges do not slide on the points of the multiple wires with which thespring 15 is to make contact. Hereby contamination of the contact pointsthrough particles which may be worn away from the insulating material ofthe plug is avoided.

With regard to the guiding of the metal bands 5 during their insertioninto the multiple field, the carriage A can be provided with anextension in the form of a thin plate 23 of insulating material havingslots 24 therein which embrace one edge of the metal bands only, asshown in Figure 3, thereby avoiding swerving or bending of the portionof the metal bands extending between the slide and the Bakelite plate 4,In order that the slide 1) shall be able to pass Without obstructionunder the plate 23, the metal bands 5 are narrower at the point wherethey are secured in the slide 1), and the latter is so dimensioned thatit can pass freely under the plate 23. A similar guiding arrangement isprovided at the outer ends of the metal bands 5 where said bands aresecured in their plugs 6. The metal bands have a reduced width even atthis point, so that the portion of the band 5 which moves rectilinearlytowards the multiple field is guided at one edge (the lower one) by anarrow slot in the bottom of an extension 25 from the Bakelite plate 4.

For connecting the flexible wipers with the corresponding stationaryfixed conductors on the selector plate 0 an ordinary cord connected to aterminal distributor 26 can be used, as indicated with dot-and-dashlines in Figure 2. Said cord can be avoided, however, if the metal bands5 are extended instead towards the left of the slide b (Figure 2) andare brought in separate loops directly to the terminal distributor 26.

As regards the guiding of the metal bands 5 by means of the plate 23projecting from the carriage, the need for said guiding device dependsof course on the thickness of the metal bands 5.

If the bands are made of steel plate, having a thickness of .15millimeter, for example, said guiding device is not needed, but evenwhen using bands being as thin as .1 millimeter the guiding device maybe dispensed with under certain contingencies, particularly if thefreely extending portions are given a curved cross-section.

As far as the motor d is concerned, said motor can be substituted, ofcourse, by another driving means, for instance by two so called steppingmechanisms which act in opposite directions.

I claim:

1. In a selector, a bare metal wire contact field, a slidable switchingmember movable to and fro in front of the contact field, a reversiblemotor for driving the said switching member, a carriage arranged at saidswitching member and movable parallel with the path thereof and inrelation thereto, a number of wipers adapted to be inserted between thewires of the multiple field, curved and electrically insulated slots insaid carriage, a number of flexible electric conductors carrying saidwipers and being slidably supported by said curved electricallyinsulated slots, means securing the conductors for movement in bothdirections with the slidable switching member, said carriage being drawnalong with the switching member in one direction of movement thereof bythe conductors, and means to temporarily lock the carriage againstmovement in the opposite direction whereby during movement of theswitching member in the second mentioned direction, the wipers at thefree ends of the flexible conductors are projected from the carriage atright angles to the paths of movement thereof and are moved in betweenthe wires of the multiple fields.

2. An automatic selector in accordance with claim 1 in which theflexible conductors have wiper-shaped free ends.

3. An automatic selector in accordance with claim 1, in which the slotsfor the flexible conductors are formed in a pressure-cast plate ofinsulating material.

4. An automatic selector in accordance with claim 1 in which those partsof the flexible conductors made in form of elastic metal bands whichextend freely outside the channels in the carriage are guided on theiredges in slots provided in an extension from the carriage.

5. An automatic selector as claimed in claim 1 in which the wipers areprovided at their outer ends with plugs having an I-shaped crosssection, the contact springs of the wipers electrically connected withthe flexible conductors being disposed between the projecting flanges ofsaid plugs whereby the flanges of said plugs while constituting a guidewith respect to the multiple wires slide across other surfaces of saidwires than those with which the contact springs make contact.

6. An automatic selector in accordance with claim 1 in which theflexible conductors made in form of elastic metal bands have thoseportions which extend outside the carriage with an armate cross section.

BERTIL JOHAN BRANDER.

